1. Field of the Invention
The present invention relates to a shock absorber adapted for use in a vehicle suspension system for vibration attenuation.
2. Description of the Prior Art
Generally, a suspension system applied to a vehicle is provided with a shock absorber constructed to cushion a shock by way of a coil spring and to prevent repeated vibrations generated during the shock buffering of the coil spring.
In other words, the coil spring serves to cushion the shock and the like from the road surface to transmit same to a body of the vehicle and the repeated vibrations according to the shock buffering action of the coil spring are attenuated to thereby maintain vehicle safety while running and to reduce swaying, such rolling, and pitching of the vehicle.
The shock absorber is dually formed, as illustrated in FIG. 5, with inner and outer tubes 50 and 51, between which there are provided a housing 53 formed with a storage chamber 52, a rod 54 arranged to pierce the inner tube 50, a piston 57 disposed at a longitudinal end of the rod 54 to divide the inner tube 50 into a first and a second chamber 55 and 56 and a foot valve 58 equipped at a longitudinal end of the inner tube 50.
Furthermore, the shock absorber is formed with a vibroisolating tube 59 to encompass an exterior surface of the outer tube 51, and a bushing 60 for connecting wheels and body (not shown) is installed at a longitudinal end of the rod 54 and at facing end of the outer tube 51. The inner and outer tubes 50 and 51 are filled with fluid (F).
The piston 57 is installed with an open/close valve 61 in order to generate an attenuating force by restricting movement of fluid (F) filled in the inner tube 50, where, the piston 57 includes, as illustrated in FIG. 6, a plurality of orifices 62 formed at the piston 57 and a plate-like open/close valve for blocking the orifices 62 during compression and for opening the orifices during expansion.
Now, operation of the shock absorber thus constructed will be described in detail. When wheels are bounced while a vehicle is running, the housing 53 connected to the wheels (suspension arms and the like) rises, by which the piston 57 moves toward a direction of compressing the second chamber 56. When the second chamber 56 is compressed by the piston 57, the open/close valve 61 maintains a closeness, where the fluid compressed in the second chamber 56 is infused into the storing chamber 52 via the foot valve 58 to thereby enable the piston 57 to descend.
When the wheels are rebounded to lower the housing 53 while the piston 57 is descended, the piston 57 is resulted to go upwards, and when the piston 57 is ascended, the open/close valve 61 blocking the orifices 62 is bent to open the orifices 62.
When the orifices 62 are opened, the fluid (F) moves through the orifices 62 to move towards the second chamber 56, where, an attenuating force is generated which is as strong as fluid resistance generated while passing through the orifices 62 and the open/close valve 61.
The open/close valve 61 is usually made of same material in plate-like shape. The attenuating force relative to speed of the piston 57 is linearly increased at a predetermined ratio but suddenly turns upwards at a strain point (V).
In other words, the attenuating force is increased relatively slow before the strain point (V) but is suddenly increased past the strain point (V). this linear ratio change of the attenuating force is caused by a phenomenon where, when the plate-like open/close valve 61 is bent to exceed a predetermined extent, resilience thereof is markedly increased, which remarkably increases fluid resistance according to the open/close valve 61, thereby changing the linear ratio of the attenuating force.